1. Field of the Invention
The present invention relates to a film bulk acoustic resonator (FBAR) filter and duplexer. More particularly, the present invention relates to a FBAR filter where at least two shunt resonators are connected in parallel and there is at least one trimming inductor therebetween so that attenuation characteristic of the filter is enhanced, and a duplexer thereof.
2. Description of the Related Art
Recently, as mobile communication devices such as mobile phones have become widely used, studies on miniaturization and weight reduction of products have been performed, as well as on an improvement of performance. Filters and duplexers are examples of components that affect the size and weight of mobile communication devices.
A filter is an element for filtering desired frequency signals from a wide frequency band and may be manufactured by producing a series resonator and a shunt resonator individually, then integrating them on a substrate mounted with a trimming inductor.
Accordingly, the size of the filter increases when each resonator is manufactured separately and subsequently attached. Additionally, the efficiency of the filter is reduced by the use of wire bonding for connecting elements and thus increasing parasitic components.
Mobile communication devices generally include a reception filter and a transmission filter. To this end, an individual filter enhances attenuation of a signal of a counterpart frequency band by raising the number of shunt resonators or by using a shunt resonator which is physically larger than a series resonator.
Furthermore, with reference to a conventional filter 100 as shown in FIG. 1, if shunt resonators 121 and 122 are larger than a series resonator 110, the filter 100 is manufactured by connecting the shunt resonators 121 and 122 to trimming inductors 131 and 132, respectively, in order to resolve the increase in the impedance of the filter 100. In the conventional filter 100 corresponding trimming inductors 131 and 132 are required for each of the shunt resonators 121 and 122, resulting in an increase in the size of the filter 100, the difficulty of the manufacturing process, and manufacturing costs.
For example, when the shunt resonators 121 and 122 and the trimming inductors 131 and 132 are connected in as the manner shown in FIG. 1, each of the trimming inductors 131 and 132 should have a capacity of approximately 2˜4 nH so that the filter 100 resonates at around 2 GHz.
Moreover, as the filter 100 requires a larger substrate to mount high capacity trimming inductors 131 and 132, a problem arises with the miniaturization of the filter 100 by the on-chip system. Additionally, when fabricating a duplexer having a transmission filter and a reception filter using a conventional filter, at least two high capacity trimming inductors should be used, resulting in an even larger increase in the size of the duplexer, the difficulty of the manufacturing process, and manufacturing costs.
Accordingly, there is a need for an improved apparatus that allows for manufacturing of smaller filter devices while allowing for a simplified manufacturing process and reduced manufacturing costs.